The present invention relates to a process for preparing a metallized resin film suitable for a condenser element, particularly to a novel process for providing a margin in a metallized resin film for a condenser element.
As one of common condenser elements, there has been known a metallized resin film which consists of a resinous layer as dielectric and a metal deposition layer provided on the resinous layer as an electrode. Such a metallized resin film has been prepared by the following two methods: one method directs to a process for preparing a metallized resin film of which thickness is comparatively large, for instance, about more than 4 .mu., which is characterized by depositing a metal on a preformed resin film such as polyethyleneterephthalate film. Other method directs to a process for preparing a metallized resin film of which thickness is comparatively small, for instance, about less than 4 .mu., which is characterized by depositing a metal on a resinous coating layer provided on a base film by coating method and then peeling off the metal deposition layer and resinous coating layer out of the base film.
On the other hand, as processes for providing a margin (which means a part where a metal deposition layer is not present on a resinous layer, for instance, an ear part of a metallized resin film) in a metallized resin film, there have been adopted tape-masking method, oil-masking method and electric-discharging method. In the tape-masking method, the margin is formed by masking the surface of a dielectric resinous layer with a film or tape in the portion of the resinous layer corresponding to a marginal pattern, depositing a metal on the whole surface of the dielectric resinous layer partially coated with the film or tape and peeling off the film or tape. In the oil-masking method, the margin is formed by coating an oil on a dielectric resinous layer in the portion of the resinous layer corresponding to a marginal pattern and depositing a metal on the dielectric resin film partially coated with the oil (in that case, the metal is not deposited to the part coated with the oil). In the electric-discharging method, the margin is formed by depositing a metal on the whole surface of a dielectric resinous layer and partially eliminating the metal deposited in the portion corresponding to a marginal pattern by means of electric-discharging.
However, the tape-masking method and oil-masking method have various disadvantages such as the complexity in the procedure of masking the surface of a dielectric resinous layer with a film or tape, or an oil so that only a part of the surface of the dielectric resinous layer to be a margin later is covered and other part of the surface of the dielectric resinous layer is not covered, and the unevenness of the metal deposition layer on a boundary line between a marginal part and a metal deposition part which is hereinafter referred to as "margin edge", which results from the peeling of metal deposition layer on the margin edge and the ununiform deposition of metal on margin edge. The oil-masking method has a further disadvantage of the lowering in a electrical property of the metallized resin film due to a oil margin.
Further, such conventional methods for forming a margin has a common disadvantage that a margin can be formed only in the longitudinal direction of the film and can not be formed in the transverse direction of the film. In the tape-masking method and oil-masking method, generally, a tape or oil for masking a dielectric resinous layer is continuously applied to the dielectric resinous layer with running the dielectric resinous layer at a constant speed. On the other hand, in the electric-discharging method, the deposited metal on the dielectric resinous layer by electric-discharging is continuously eliminated with running the metallized dielectric resinous layer at a constant speed. In that case, it is possible to form a margin only in the longitudinal direction of the film but it is impossible to form a margin in the transverse direction of the film and further a margin having an arbitrary pattern. If it is tried to obtain at any cost a metallized resin film having a margin consisting of a margin in the longitudinal direction thereof and a margin in the transverse direction thereof by conventional methods, it would be necessary to stop the running of the film in the longitudinal direction thereof during the operation of masking the film with a tape or oil in the transverse direction thereof, or of eliminating the metal deposition layer on the film in the transverse direction thereof by electric-discharging. However, such a procedure is much tedious and therefore the operating efficiency is remarkably reduced. Thus, in conventional metallized resin films, the marginal pattern thereof was restricted to only that formed in the longitudinal direction of the film.